Known linkage systems utilizing fluid cylinders for changing link length and angular orientation typically utilize controls wherein information relating to the length and/or velocity of movement of one or more cylinder rods is required. The electrical aspects of control apparatus for such systems typically require the use of a variety of sensors, including, but not limited to, lever position sensors and linkage position sensors, and also utilize electro-hydraulic valves and an onboard electronic control module operable for executing a control strategy for linkage movement. A central portion of such control strategies is typically a linkage position input which can be embodied, for instance, in positional and/or velocity information for a cylinder rod. Such positional and velocity information is typically collected by a position sensor mounted on or in a subject fluid cylinder or on a linkage, and through the linkage kinematics one can translate linkage angle into cylinder length. Reliable data collection from such sensors has been found to be largely dependent on the ability to maintain the integrity of such sensors and the conductive element or other path of communication between the sensor and the system under adverse operating and environmental conditions, such as heat, cold, dust, dirt, and contact with rocks and other objects that can damage the sensor and/or its path of communication with other elements of the control system.
Currently, to reduce the potential for damage to sensors from such operating and environmental factors, the sensors themselves are sometimes located within the cylinder housing or body. Reference in this regard, Chan et al. U.S. Pat. No. 5,977,778 issued Nov. 2, 1999 and assigned to Case Corporation of Racine, Wis., which discloses a method and apparatus for sensing piston position including a transmitter/receiver unit mounted on a cylinder housing in communication with an internal cavity thereof for sensing the position of a piston of the cylinder and communicating via a conductive path to circuitry located externally to the cylinder for processing the signal data and generating an output signal representative of the piston position. Reference also Tellerman U.S. Pat. No. 4,952,873 issued Aug. 28, 1990 and assigned to MTS Systems Corporation of Eden Prairie, Minn., which discloses a compact head, signal enhancing magnetostrictive transducer mounted on a mounting head positionable in a tank, cylinder or the like for sensing a piston position or liquid level, which transducer is connected via one or more conductive paths to electronic circuitry for providing output signals indicative of a displacement. However, known systems such as these have been found to provide only a partial solution to the problems encountered as electronic components required for the operation of the sensors and transducers thereof remain externally located, and as a result sensor inaccuracies and even worse sensor failure is likely due to the cylinder and sensor being subjected to adverse operating and environmental factors.
Moreover, it is typically required that the cylinder be physically robust and possess the ability to repeatably transfer a significant load between the ends of the cylinder. Such usage is common to implement bearing earthmoving machines, compactors and rams to name just a few. To ensure that the loads are suitably transferred by the cylinder in physically demanding environments which are associated with such cylinder usage, the cylinders are often unitary and may have limited bolted or removable joints.
Accordingly, it is customary to use a cylinder body which includes a pair of end caps and is adapted to receive a rod therein. At least one of the end caps is typically bolted to the tube or cylinder body to provide proper transfer of force between the cylinder ends, in a trunnion mount cylinder design. Another type of cylinder is a clevis mount cylinder which includes a body and a piston and rod assembly therein. However, the end caps are generally welded to the body making the cylinder a unitary element and one which is often not readily serviceable without removing the cylinder from the machine or linkage to which it is attached.
In view that many cylinder applications require robust usage which include suitable operation even if the cylinder is prone to impact and abrasion from rock, earth, slag, debris, etc. during use, in combination with the requirement that the cylinders include the ability to transfer significant force loads therethrough, it may be unacceptable to position the sensor or sensor electronics outside of the cylinder body even if an impact shield is positioned thereover. Further, cylinders such as trunnion mount designs may better facilitate service to a sensor mounted within the cylinder.
Moreover, if it is attempted to at least partially conceal the sensor and/or sensor electronics within a sturdy outer structure, then it is often difficult to easily access the position sensor or sensor electronics when service is required. Unfortunately, if a position sensor needs to be serviced or replaced, it is often necessary to replace the entire cylinder unit at a significant expense to the machine owner or operator.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.